In arid areas of the world water is becoming one of the most precious natural resources. Meeting future water needs in these arid areas may require aggressive conservation measures, irrigation systems that apply water to a landscape based upon calculated water requirements of the plants. Many irrigation controllers have been developed for automatically controlling application of water to landscapes. Known irrigation controllers range from simple devices that control watering times based upon fixed schedules, to sophisticated devices that vary watering schedules according to local geography and climatic conditions.
In the simpler types of irrigation controllers, a homeowner typically sets a watering schedule that involves specific run times and days for each of a plurality of stations, and the controller executes the same schedule regardless of the season or weather conditions. From time to time the homeowner may manually adjust the watering schedule, but such adjustments are usually made only a few times during the year, and are generally based upon the homeowner's perceptions rather than actual watering needs. One change is often made in the late Spring, when a portion of the yard becomes brown due to a lack of water. Another change is often made in the late Fall when the homeowner assumes that the vegetation does not require as much watering. These changes to the watering schedule are typically insufficient to achieve efficient watering.
More sophisticated irrigation controllers use evapotranspiration rates for determining the amount of water to be applied to a landscape. Evapotranspiration is the water lost by direct evaporation from the soil and plant and by transpiration from the plant surface. Potential evapotranspiration (ETo) can be calculated from meteorological data collected onsite, or from a similar site. One such system is discussed in U.S. Pat. No. 5,479,339 issued December, 1995, to Miller. Due to cost considerations, most of the data for ETo calculations is gathered from off-site locations that are frequently operated by government agencies. Irrigation systems that use ETo data gathered from off-site locations are discussed in U.S. Pat. No. 5,023,787 issued June, 1991, and U.S. Pat. No. 5,229,937 issued July, 1993 both to Evelyn-Veere, U.S. Pat. No. 5,208,855, issued May, 1993, to Marian, U.S. Pat. No. 5,696,671, issued December, 1997, and U.S. Pat. No. 5,870,302, issued February, 1999, both to Oliver.
Due to cost and/or complicated operating requirements, very few of these efficient ETo based irrigation controllers are presently installed at residential or small commercial landscape sites. Consequently, most residential and small commercial landscape sites are irrigated by controllers that provide inadequate schedule modification. This in turn results in either too much or too little water being applied to the landscape, which results in both inefficient use of water and unnecessary stress on the irrigated plants. Thus, a need exists for a cost-effective irrigation system for residential and small commercial landscape sites that is capable of frequently varying the irrigation schedule based upon estimates of actual water requirements. This need was satisfied to a large extent for newly installed irrigation systems by devices and methods disclosed in pending U.S. patent application Ser. No. 09/082,603. However, there are many thousands of irrigation controllers already installed that could benefit from more sophisticated irrigation techniques without requiring complete replacement.
To that end devices are already known that can be connected to existing irrigation systems to provide automatic adjustments to the irrigation schedule. Unfortunately, most such devices merely interrupt complete irrigation schedules based upon a single simplistic parameter such as detection of rain or excessive soil moisture. Examples of rain sensors are found in U.S. Pat. No. 4,613,764, issued September, 1986 to Lobato, U.S. Pat. No. 5,312,578, issued June, 1994 to Morrison et. al., U.S. Pat. No. 5,355,122 issued October, 1994 to Erickson, and U.S. Pat. No. 5,101,083, issued March, 1992 to Tyler, et al. Irrigation interrupters are also known that utilize other factors, including temperature extremes, high light intensity, high winds, and high humidity. See e.g., U.S. Pat. No. 5,839,660, issued November, 1998 to Morgenstern, et al., U.S. Pat. No. 5,853,122, issued December, 1998 to Caprio, U.S. Pat. No. 4,333,490 issued June, 1982 to Enter, SR., and U.S. Pat. No. 6,076,740, issued June, 2000 to Townsend. However, as mentioned above, all of the known devices interrupt the operation of one or more full irrigation schedules.
Thus, there is still a need for cost effective devices and methods that automatically modify the run times of irrigation schedules of installed irrigation controllers.